I would listen to these guys if I was you. I haven't shot a Red Deer or any other deer for that matter, but these men know their hunting and the pics they have posted over the years is the proof of their proficiency.
With that fast twist barrel you can use a heavier conical. Conical loading is supposed to be allot faster and easier than a PRB. So you need a new bullet supply or a new mold. Only the first setting of the conical past the muzzle is supposed to be 'hard', after it clears the muzzle just a slight push should be all that you need to seat the bullet. Use a tight fitting over bullet card and you shouldn't have an issue with the bullet creeping off the powder.
With that fast twist barrel you can use a heavier conical. Conical loading is supposed to be allot faster and easier than a PRB. So you need a new bullet supply or a new mold. Only the first setting of the conical past the muzzle is supposed to be 'hard', after it clears the muzzle just a slight push should be all that you need to seat the bullet. Use a tight fitting over bullet card and you shouldn't have an issue with the bullet creeping off the powder.